The article "Cordless telephones and cellular radio: synergies of DECT and GSM" by W. H. W. Tuttlebee in Electronics and Communications Engineering Journal, October 1996, pages 213 to 223 discusses the interest among fixed or wireline telecommunications operators to provide some telecommunication services by radio links and the interest among mobile telephone service operators to provide a complete range of services in order to compete with the traditional fixed telecommunication systems. The present invention relates to the integration of fixed and mobile telecommnunication services. Conventionally this integration is limited to the provision of single-number routing regardless of location, i.e. to provide mobility of the subscriber anywhere within a geographical area and independent of the transmission system of messages to the subscriber. Such schemes involve the co-operation of one or more of fixed, cellular radio or cordless telephone networks.
Despite this interest in integration of the various systems two basic philosophies still exist as to how a telecommunications network is to be organized. The older of these two systems switches calls through to a particular location. This type of system is well known as the "Plain Old Telephone System" ("POTS"). In an implementation of land lines the service is generally tied to the access method. Service provisioning, customer service and problem resolution are tailored to the idea that access and service are tied together. The physical management of the large number of subscriber loops served by the network depends upon this mapping. Subscribers are provided with a directory number for a location in the system, i.e. to a connection point and not for a particular receiving device. Modifications to such conventional systems are known, e.g. fixed radio access known from the article by R. Dettmer, in the IEE Review from July, 1995, pages 145 to 148. Such radio access is merely the substitution of one leg of the transmission path of a single telecommunications network with a radio link but is not the integration of two networks.
On the other hand, the more modem mobile telephone telecommunication systems allow call routing to a particular device independent of its location provided it is within the radio coverage area of the system. To be able to locate a receiving device, an electronic means for identifying the device and thereby indirectly the subscriber, is provided in the receiving device. This identification may be in the form of information stored in a memory which is part of the mobile receiving device itself or it may be in a separate insertable memory module, for instance a Subscriber Identity Module (SIM) in an integrated chip card as is known from the European GSM mobile telecommunication system. The radio telecommunication system protocols are used to identify a user from the SIM's encoded information, and the services to which the user has subscribed can be derived from the same stored information.
The issue of mobility is traditionally considered to be of very great importance. For instance two major research projects, the Future Public Land Mobile Telecommunication System (FPLMTS) of the CCIR Committee TG 8/1 and the Universal Mobile Telecommunications System (UMTS), which is part of the European RACE program, have the common goals of providing international roaming by mobile users, of providing service quality equivalent to fixed-line telecommunication systems and of providing some ISDN services.
Certain types of data transmission, e.g. fax, may pose technical problems with mobile phones. Modem generated tones have gaps and strong phase changes due to rapid multipath fading. This results in data being garbled or lost. Further, handoffs between cells of the mobile telecommunications system are an even stronger cause of data loss. This problem cannot be completely solved by using a stationary receiving device. In large cities such as Paris, France, handoffs can be expected within the normal duration of a fax message even if the faxing device is stationary. These handoffs are forced because of changes in the signal intensity caused by such variables as moving traffic, swinging cranes on building sites and the need to readjust the boundaries of cells in order to cope with load changes and the limitations of the frequency spectrum available. Further, the bandwidth of a mobile telephone system is usually very limited whereas wireline connections may carry 100 kb/s or higher. Hence, for some types of traffic a mobile phone subscriber may prefer an alternative type of connection.
A subscriber may wish to have all e-mail messages or faxes sent and received by a device which is not subjected to handovers and/or has a higher transmission rate. This could be achieved by automatically directing a call to a fixed telephone in a conventional (POTS) wireline telephone system. This approach has the disadvantage that the subscriber must subscribe to both the wireline and the wireless system. The subscriber may wish to make use of reductions in charges resulting from using one system for all services, rather than have to subscribe to two systems. One possible way of solving this problem would be for the radio telecommunications system provider to put in a wireline system as well as the radio telecommunications system and thus be able to offer both types of service, i.e. mobile telephones and fixed transceivers such as fax machines. This has the disadvantage that the provider must install and maintain two differing sets of equipment.
To achieve an integration of a wireless and a wireline system it is preferred if: a. the subscriber loops (belonging to the wireline system) can be tracked to the subscribers service for problem resolution, routine maintenance, and any possible regulatory requirements; b. the subscriber's SIM information is available to the wireless network transparently, as anything less would require changes to the wireless network traffic model.